The two are interrelated. I always thought Chaos was sexier but fractal theory was more important.

Chaos theory always seemed to be a consequence of quantum indeterminism. The electron is everywhere and nowhere until you look. Its location a matter of probability.

The collapse of the cloud of probabilities into a "reality" is basically the moment that "Chaos" comes into play. The most probable outcome is the most likely. But, Chaos determines the exact details.

Fractal Theory speaks to the actual nature of how the Universe self organizes. Much more important.